It is not uncommon for patients undergoing therapeutic medical treatment to receive frequent vascular injections or infusions of therapeutic fluids. Other medical treatments require frequent withdrawal or infusion of blood. There are many other medical circumstances which require chronic vascular access. They include therapeutic requirements for the following: neonatal umbilical vein cannulation, hyperalimentation, chemotherapy, permanent intravascular site for portable drug infusion devices, other drug therapy such as osteomylitis and fungal infections, blood pressure monitoring, hemodialysis, plasmapherisis, and repeated blood sampling.
In the past, such chronic infusions or blood withdrawals required repeated punctures through the skin. Today, most of these procedures are performed using percutaneously placed or cannulated intravascular catheters. Examples include the implantable catheter disclosed by Anderson et al. (U.S. Pat. No. 4,536,179) which discloses a catheter for long term implantation. This catheter is made of a flexible, inert, nontoxic and biocompatible polymeric material having a thin flurocarbon coating, achieved by glow discharge plasma polymerization on at least one of the contacting surfaces which prevents self-adhesion of the cured polymer surfaces.
Examples of other catheters include central venous catheters generically termed subclavian catheters. Intravascular access catheters in this category are generally made of plastic or rubber tubes with female luer fittings at one end. Catheters of this type are usually selected for short-term therapy. In order to extend the useful life if this type of catheter, the catheter lumen is often filled with a solution containing an anticoagulant between uses (e.g., heparin). This is necessary in order to prevent blood from coagulating in the catheter lumen, thereby occluding the catheter and preventing its further use. Since the anticoagulant constantly diffuses from the lumen into the blood stream, however the catheter must be refilled with the anticoagulant solution every 2-3 days in order to prevent a clot from forming in the catheter tip.
This problem has been circumvented to a certain degree by the Shiley Vas-Cath Catheter (Shiley, Inc., Irvine, CA) which is a transcutaneous subclavian catheter which differs from the prior art subclavian catheters in that it is essentially two coaxial tubes with the inner tube being removable. Each time a catheter clots off, the inner tube, which contains the clot, is extracted from the outer tube and replaced with a fresh inner tube.
Another solution to the problem of clotting in the catheter lumen, involves the insertion of a solid flexible plastic rod or obturator into the catheter lumen between uses. The obturator completely occupies the catheter lumen, thereby preventing the diffusion of blood into the lumen where it might subsequently form a clot.
Medical procedures requiring long-term vascular access, however, require totally implantable products in order to limit the risk of infection. Several implantable devices have been designed which provide a metal or plastic housing containing a rubber septum which is specially constructed to undergo repeated punctures. Unfortunately, there catheters have no features to prevent clotting by blood components other than their small lumen diameters which provide some limitation on the diffusion of blood into the lumen. Although these catheters are generally filled with a solution containing an anticoagulant between uses, if the time interval between catheter uses is relatively long (e.g. weeks instead of days), each therapy session must be initiated by blowing the clotted material into the vasculature. Obviously, this is not particularly desirable as the blood clot may initiate further clotting and could possibly result in an embolism or other serious vascular disorder.
Unfortunately, Shiley Vas-Cath Catheter discussed above and other designs featuring solid removable obturators, are not suited for total implantation. This is because such a modification would require a relatively large solid element to be passed through the skin, subcutaneous tissure, and catheter septum with each use.
Diffusion or aspiration of blood into the catheter may be prevented by adding a check valve to the intravascular tip of the catheter. Such a check valve is disclosed in Dorman U.S. Pat. No. 4,657,536) which describes a sleeve-type one-way check valve design for this purpose. While this design prevents blood components from clotting the tip, it allows only infusion of liquids and does not allow withdrawal of blood samples which is often desirable maneuver to be carried out with intravascular access catheters.
A two-way check valve located at the tip of the catheter is less susceptible to clotting and allows for infusion of fluids as well as the withdrawal of blood samples. One commercially available percutaneous catheter which has a two-way check valve is the Groshong Catheter (Catheter Technology Corp., Salt Lake City, UT). This catheter features a slit valve at the tip of the catheter which allows both aspiration of blood and infusion of fluids and yet precludes the diffusion of blood components into the lumen between therapy sessions. Although this catheter is currently a percutaneous appliance, it would be conceivable to make such a catheter into an implantable device by replacing the female luer fitting with an implantable septum. The major drawback to slit valve check valves, however, is unreliability, which bodes poorly for long term use. Their "valving" performance depends upon the elastic forces within the catheter wall. These forces must be strong enough to return the valve to the relaxed or closed position between uses. Construction of the device with a tight fitting closed state results in a stiff catheter in which reliability is achieved at the expense of mechanical flexibility and bio-incompatibility with respect to interaction between the catheter and the endothelial lining of the vessel being cannulated.
It will be appreciated from the foregoing that prior art devices present problems which are in need of solutions. The present invention provides solutions for these and other problems.